The present invention relates generally to aircraft cabin pressure control systems, and more specifically to an all electric aircraft cabin pressure control system controlling a plurality of outflow valves providing for exhaust flow biasing.
For a given airspeed, an aircraft may consume less fuel at a higher altitude than it does at a lower altitude. In other words, an aircraft may be more efficient in flight at higher altitudes as compared to lower altitudes. Moreover, bad weather and turbulence can sometimes be avoided by flying above such weather or turbulence. Thus, because of these and other potential advantages, many aircraft are designed to fly at relatively high altitudes.
As the altitude of an aircraft increases, the ambient pressure outside of the aircraft decreases and, unless otherwise controlled, excessive amounts of air could leak out of the aircraft cabin causing it to decompress to an undesirably low pressure. If the pressure in the aircraft cabin is too low, the aircraft passengers may suffer hypoxia, which is a deficiency of oxygen concentration in human tissue.
Studies have shown that the symptoms of hypoxia may become noticeable when cabin pressure altitude is above the equivalent of 8,000 feet. Thus, many aircraft are equipped with a cabin pressure control system to, among other things, maintain the cabin pressure altitude to within a relatively comfortable range (e.g., at or below approximately 8,000 feet) and allow gradual changes in the cabin pressure altitude to minimize passenger discomfort and maintain cabin-to-atmosphere differential pressure below nominal and maximum limits. Thus, many cabin pressure control systems control cabin altitude as a function of aircraft altitude, and do so in a manner and rate that will keep the cabin-to-atmosphere differential pressure less than the nominal limit.
To maintain aircraft cabin altitude within a relatively comfortable range, cabin pressure control systems may be equipped with an outflow valve. An outflow valve may assist in controlling cabin pressure by regulating air flow out of the cabin. One particular type of outflow valve that may be used is a butterfly outflow valve. A butterfly outflow valve typically includes a flapper or gate, which is typically used as the control element to regulate the flow of air out of the cabin. More particularly, the flapper is coupled to a shaft that is rotationally mounted to the outflow valve body. An actuator, which is coupled to the shaft, positions the flapper element in response to commands from a controller to thereby regulate the air flow out of the cabin.
Conventional cabin pressure control systems are designed to exhaust cabin air during flight in order to comfortably and safely pressurize the fuselage (cabin) so that high altitude aircraft flight can occur. Cabin pressure control systems have used pneumatic, pneumatic-electric, and more recently all electric control systems. Typical CPCS designs have utilized a single electromechanically controlled outflow valve that is modulated to control the outflow of air from the cabin, thereby controlling cabin pressure. The electromechanically controlled outflow valve may be comprised of an embedded software controller that spins a motor which drives a geartrain connected to a butterfly valve.
As can be seen, there is a need for aircraft having more than a single outflow valve and an all electric cabin pressure control system for controlling multiple outflow valves.